Vol II, Chapter 1 of the Feynman Lectures explains why negative electrons do not get closer to the positively charged nucleus despite the great attractive force:
If we try to confine our electrons in a region that is very close to the protons, then according to the uncertainty principle they must have some mean square momentum which is larger the more we try to confine them. It is this motion, required by the laws of quantum mechanics, that keeps the electrical attraction from bringing the charges any closer together.
Why can't this same argument be applied to the particles in the nucleus? I.e, why can we pinpoint the positions of adjacent protons and neutrons even though this would mean that their momentums are more uncertain and thus moving in such a way that they couldn't be co-residing in a nucleus?